Device for generating constant voltage at variable speed



Sept. 7, 193 7. MAG 2,092,213

DEVICE FOR GENERATING CONSTANT VOLTAGE AT VARIABLE SPEED Filed June i0, 1935 a Sheet-Sheet 1 &

Se t. 7, 1531. M 2,092,313

DEVICE FOR GENERATING CONSTANT VOLTAGE AT VARIABLE SPEED Filed June-l0, 1935 s sheets-sheet 2 Sept. 7, 1937. 2,092,213

DEVICE FOR GENERATING CONSTANT VOLTAGE AT VARIABLE SPEED Filed June 10, 1935 3 Sheets-Sheet 3 (fig- DP/ V/NG SHAFT cab-M1 22, M, m; 4M I Patented Sept. 7, 1937 UNITED STATES DEVICE FOR GENERATING CON STANT VOLTAGE AT VARIABLE SPEED Toshiichi Inagi, Hitachi-cho, Japan, assignor to Kabushiki-Ka'isha Hitachi-Seisakusho, 'lohio,

Japan, a corporation of Japan Application June 10, 1935. Serial No. 25,955

- In Japan July 10, 193

9 Claims. (01. I'll-223) This invention relates to improvements in a device for'generating constant voltage at variable speed, such as a generator for use on car axles. comprising a main generator whose field winding is fed by two exciters in series with opposing electromotive forces, of which one is the main exciter of saturated characteristic and the other is the auxiliary exciter of unsaturated characteristic.

The invention embodies the 'provision on the said auxiliary exciter of another field winding fed by the combined electromotive force of the twoexciters in series and in opposed relation to original field winding thereof. 1

The main object of the invention is to obtain a generator which is able to generate a more constant voltage than has been possible heretofore at a reduced size of the machine.

Other objects and features of the invention will be understood from the following descriptions and the accompanying drawings, in which, Fig. 1 shows an electrical connection of the device according to the invention.

Figs. 2 to4 are diagrams for explaining the performances of the device. 7

Fig. 10 is a schematic view showing a modified arrangement.

Fig. 11 is a schematic view of a circuit embodying a modification of the invention.

Fig. 12 is a similar view illustrating a further modification of the present invention.

Referring to Fig. 1, G is a main generator having a separately excited field winding F. E1

f: and j: of the auxiliary exciter E1 act diifer-,

entially. On the other hand, the electromotive force of the main exciter E1 is additive with the electromotive force of the auxiliary exciter E: as induced by the field winding {3, but is differential with the electroniotive. force induced by the field winding f2. These relations are shown by' arrow heads in Fig. 1. The main exciter E1 has a saturated characteristic, while the auxiliary exciter E: has an unsaturated characteristic. The generator G and the two exciters E1 and E: are mechanically connected directly with one another and with a driving shaft.

Figs. 5 to 9 show modifications of the invention.

is a main exciter having a field winding f1, and

windings F and I: being connected in parallel- To simplify the explanation, first the performance of the device in which the field winding is is not provided will beexplained with reference to Fig. 2. In this figure, V1 shows the saturation curve of the exciter E1 at a. certain h, Thenthe point of intersection a of the line DB1 and the generator voltage curve V; represents the terminal voltage of the main generator at this particular speed. -When the speed increases, all the voltages including the exciter voltage V; and the generator voltage V; increase correspondingly. Thus ata certain increased speed, the curve of the main generator voltage assumes the position represented by V'I, and the generator voltage will displace from the point a to the point b.

In order to make the increase of the generator voltage, which takes place when the speed is increased, sufiiciently small, the resultant exciting voltage curve Va and, consequently, the generator voltage curve V; at the lowest working speed u must have as steep fronts as possible at the neighborhood or the point 0, where the vertical line passing through the point of intersection of V1 and V curves meets the abscissa. This requires that the exciter voltages V1 and V: must both be'very high in comparison to the resultant exciting voltage V9 and this fact inevitably-leads to the disadvantage that thesize and weight of the exciters are increased. These disadvantages are effectively obviated according to the invention by providing on the auxiliary exciter E: another exciting winding 1: acting differentially-to the first winding I: and choosing the intensity of excitation of the said field winding la within certain predetermined limits. The

effect of such field winding fa will be described Referring to Fig. 3, V1is the saturation curve.

at a certain speed of the main exciter E1, the

magnetic circuit of which is suificiently saturated, and Vi is the saturation curve of the auxiliary exciter E: when it is excited only by .the'field winding is. If we assume, for the sake of simplicity, that the magnetic path of this exciter V as of ideally unsaturated, the curve V: will be a straight line. Let m represent the-point of intersection of two curves V1 and V2.

ing f2, and m be the number of turns thereof, and let I3 and m be the corresponding figures .oi the winding f3. Then at a certain magnetomol tive force I2n2=0y of the winding f2, the counteracting magnetomotive force Iana=y":r' of the winding is will be prevailing at the same time, so

that the resultant efiective magnetomotive force ference between yz and 22's, evidently is the resultant exciting voltage acting across the winding is. Let R: be the ohmic resistance of the winding is. Then ye will be equal to the I3R3. So that we-have It will thus be seen that the tangent of the angle (p is constant but varies directly with the resistance of the exciting circuit is and inversely with-the number of turns. In other words, this angle decreases when the intensity of excitation of the field winding is increases. Let us now draw throughthe origin 0 a line 0R3 parallel to the line are, and call it a-line of ohmic drop across the field .winding fa. Then we can conclude that the saturation curve V3 of the auxiliary exciter E2 may be obtained as the locus of the point y of, right angled triangles drawn across two saturation curves V1 and V2 with its hypothenuse we parallel to the said line of ohmic drop 0R3.

It will easily be.seen from Fig. 3 that when the angler 1 is equal to the angle 0, which is the angle of inclination of the saturation curve V2 to the horizontal line, the ohmic drop line as- 25 tan Lyxz=tan l .45 sumes the position ORa, and the curve V3 is reduced to a vertical line Viiv passing through the point m. At such an intensity of excitation of the field winding 73, which may be called the critical field intensity, theoretically only one magnetomotive force 00' is possible. At, any other current 12, the performance of the device is unstable. In actual cases, however, the'-satura-- tion curve V2 is never a true straight line, especially at high magnetomotive forces,'so that the device operates quite stably even at other excitations than'OO.

At an increased excitation of the field wl'nd i ing fa, or at a smaller angle such as corresponds to the lineORK'a, the saturation curve assumes the position indicated by V "a. In this case, the

performance of the machine is unstable theoretically at a magnetomotive force which is smaller than 00'. voltages are represented by Ve, Ve and Va" in Fig. 3. Y

Thus it will be seen that the characteristics of the resultant exciting voltage can be regulated at will by varying the intensityoiexcitation of the field winding is.

The foregoing discussion relates to the case when the intensity of excitation of the field winding is is varied at a constant speed of rotation. Conversely, let us now consid'er the case when the intensity of excitation of the field windingja,

that is, the inclination of the ohmic drop llne Let 12 be the current flowing in the field wind- The respective resultant exciting 0R3, is kept constant, while the speed is varied. When the speed is increased, the angle of inclination of the line V2 increases (tan 0 varies proportionally with the speed) while the inclinasulting to the increased efiect of the field 1:.

Referring to Fig. 4, let V21 and Ve2 be the resultant exciting voltages corresponding respectively to speeds m and n2 (n2 is greater than 11.1) when the intensity of excitation of the field winding is is OR; (Fig. 3), and similarly let V21" and V82 be the resultant exciting voltages at like respective speeds, when the intensity of the field winding 13 is 0R3". 'Let V 1, Vgfl, and V"gi, V"gz be the voltages of the main generator G corresponding to the resultant exciting voltages Vel, V82, and V"e1, V"e2 respectively.

The voltage of the main generator G, for example Vgl, is substantially proportional to the product of the resultant exciting voltage (vel) and the corresponding speed (111). Let 0R1 be the ohmic drop line of the field windings f1 and is. Then the points of intersection a, b, a, b"

of the voltage curve V81, V82, V 1, V"g2 and the line 0R1 represent the respective voltages of the generator G. i

As is clear from Fig. 4, when the intensity' of' excitation of the field winding is is below the critical intensity,the exciting voltage curve VeZ corresponding to the higher speed 112 is above the exciting voltage curve Vel corresponding to the lower speed n1 so that the generator voltage V82 being proportional to mVez departs considerably from the voltage V81, which is proportional to "rival.

On the contrary, when the intensity of excitation of the field winding is is abovethe critical intensity, the excitingivoltage curve V"e2 corresponding to the higher speed n: is below the exciting voltage curve V"el corresponding to the lower speed n1, so that the effect due to the increase ofspeed is effectively compensated by the decrease .qf the resultant exciting voltage and the generator voltage curve V" i and V"2 are situated closely to each other.

It will be seen,.therefore, that the voltage regulation is better when the strength of excitation of the field winding is is higher than the critical intensity. When the speed is sumciently low, however, the regulation is fairly good even when the strength of excitation of field winding is 'is below the critical value.

According to'this invention. therefore, the

intensity of-excitation of the field winding ,1: is

chosen in relation to the extent of variation of speed in such a manner that the eflect of the latter is compensated in efiect by the variation in the excitation of .,the main generator, so that the voltage of the generator is maintained practically constant.

' In the above descriptions,-the magnetic path of the auxiliary exciter E2 has been assumed as absolutely "unsaturated, but the same reasoning of course holds approximately even when this assumptionis not strictly correct.

The device mentioned above is merely one embodiment of this invention and, of course, it may be modified in various ways without departing from the spirit of invention set forth in the appended claims. For example, two separate exciters above'mentioned may be replaced by an exciter E of'such construction in which the armatures of two exciters are combined into one rotor rotating in two independent fields (Fig. 5). Also modifications may be made in the following manners:

5 .The field windings f3 and F may be connected in serlesiFig. 6).

The generator G and the exciters Ei'and Ez' may be separately driven by a suitable prime mover (Fig.7) or by suitable prime-movers main- 10 taining a fixed speed relation with one another (Fig. 12).

r The field windings l1 and I: may be connected in parallel and connected to the terminals of the generator G (Fig. 8).

15 The field windings f1 and I: may be excited by a suitable source of constant voltage, instead of by the generator G (Fig. 9).

Moreover, with a view to cohtrolling the voltage characteristics and to increase the stability of operation, a suitable rheostatic or other controlling means RH may be provided to any or all of said field windings (Fig. 8). Also a material having a suitable temperature coeificient may be .used for resistance of said rheostats for compensating the variation in the characteristics due to the variations in temperatures. If desired} the main generator may be made so that it is either of overcompounding or-undercompounding characteristic. For example, if a resistance is connected in the main generator circuit as shown in Fig. 10 and the terminals of the fields Ii and f: are connected across the main generator and the resistance, the main generator will have an overcompounding characteristic (Fig.

10) On the other hand, if these fields are di- 7 rectly connected to the terminals of. the generator, it will have an undercompounding characteristic (Fig. 11).

What I claim is:.

40 1. Device for generating constant voltage at variable speed comprising a main generator and an exciter with two separate field systems, the said generator and exciter being arranged so as to be driven at predetermined relative speeds, in

said device the said main generator is excited by the resultant voltage of said exciter, in which one of the field systems is excited by a substantially constant voltage and is magnetically sufficiently saturated and the other is 01' a low magnetic saturation and has two field windings acting diiIerentially to each other, one of which is excitedby a substantially constant voltage in opposite polar relation to the excitation of the first field system and the other is excited by the resultant voltage of the exciter in additive polar relation with the excitation of the said first field system, and the intensity oi the last mentioned-excitation is of such a value that the variation in said resultant voltage due to the variation of the driven speed is adapted to maintain the voltage of the main generator substantially constant.

, 2. Device for generating constant voltage at variable speed comprising a main generator, a

main exciter and an auxiliary exciter arranged so as to be driven at predetermined relative speeds, in which saidm'ain generator is excited by the resultant voltage of said two exciters, of which the main exciter is excited by a substantially constant voltage and is magnetically sut- 'ficiently saturated, and the auxiliary exciter is ot a low magnetic saturation and has two field windings acting difl'erentially to each other, one

oil which is excited by a substantially constant 7 voltage in opposite polar relation to the excitation of the main exciter and the other is excited by the resultant voltage of the two exciters in additive polar relation with the excitation of the main exciter, and the intensity of excitation of the last mentioned field winding of the auxiliary exciter is of such a value that the variation in said resultant voltage due to the variation of the driven speed is adapted to maintain the voltage of the main generator substantially constant. V

3. Device for generating constant volt- I age at variable speed comprising a main generator, a main exciter and an'auxiliary exciter arranged so as to be driven at predetermined relative speeds, in which said main generator is excited by the resultant voltage of said two exciters. of which the main exciter is excited by a substantially constant voltage and is magnetically sufiiciently saturated, and the auxiliary exciter is of a low magnetic saturation and has two field windings acting difierentially to each other, one of which is excited by a substantially constant voltage in opposite polar relation to the excitation of the main exciter and the other is excited by the exciting current of the main generator in additive polar relation with the excitation of the main exciter, and the intensity of excitation of the last mentionedv field winding of the auxiliary exciter is of such a value that the variation in said resultant voltage due to the variation of the driven speed is adapted to maintain the voltage of the main generator substantially constant.

4. Device for generating constant voltage at variable speed'comprising a main generator and a v main andan auxiliary exciters directly coupled to the said main generator, in which said main generator is excited by the resultant voltage of said two exciters, of which the main exciter is excited by a substantially constant voltage and 4 is magnetically sufiiciently saturated, and the auxiliary exciter is of a low magnetic saturation and has two field windings acting difierentially to each other, one of which is excited by a substantially constant voltage in opposite polar re- 4 lation to the excitation of the main exciter and the other 'is excited by the resultant voltage of the two exciters in additive polar relation with the excitation of the main exciter, and the intensity oi excitation of the last mentioned field 5 winding of the auxiliary exciter is of such a value ot a low magnetic saturation and has. two field a windings acting difierentially to each other, one of which is excited by said substantially constant voltage inseries with the field winding of said main exciter and in opposite polar relation to the excitation oi the main exciter and the. other is 7 excited by a current corresponding to the resultant voltage of the two exciters in additive polar relation withthe excitation of the main exciter, and the intensity of excitation ofthe last mentioned field winding of the auxiliary ex- 7 6. Device for generating constant voltage at variable speed comprising a main generator, a main exciter and an auxiliary exciter arranged so as to be driven at predetermined relative speeds, in which said main generator is excited by the resultant voltage of said two exciters, of which the main exciter is excited by a substantially constant voltage and is magnetically suificiently saturated, and the auxiliary exciter is of a low magnetic saturation and has two field windings acting differentially to each other, one of which is excited by said substantially constant voltage in parallel with the field winding of said main exciter and in opposite polar relation to the excitation of the main exciter and the other is excited by a current corresponding to the resultant voltage of the two exciters in additive polar relationwith the excitation of the main exciter, and'the intensity of excitation of the last mentioned field winding of the auxiliary exciter is of such a value that the variation in said resultant voltage due to the variation of the driven speedis adapted to maintain the voltage oi the main generator substantially constant.

'7. Device for generating constant voltage at variable speed comprising a main generator,- a main exciter and an auxiliary exciter arranged so as to be driven at predetermined relative auxiliary exciter is of a low magnetic saturation and has two field windings acting differentially winding of the auxiliary exciter is of such a value that the variation in said resultant voltage due to the variation of the driven speed is adapted to maintainthe voltage of the main generator substantially constant.

8.-Device for generating constant voltage at variable speed comprising a main generator, a resistance connected in series with said main I generator, a main exciter and an auxiliary exciter arranged so as to be driven at predetermined speeds relatively to each other and to the main generator, in said device said main generator is excited by the resultant voltage of said lation with the excitation of the main exciter,.

the main generator having an under-compounding. characteristic.

9. Device for generating constant voltage at variable speed comprising a main generator and an exciting system with two separate field systems, the said generator and exciting system being arranged so as to be driven at predetermined relative speeds. in said device the said main generator is excitedby the resultant voltage of said exciting system in'which one of the field systems is excited by a substantially constant voltage and is magnetically sufiiciently saturated and the other is of a low magnetic saturation and has two field windings acting differentially to each other, one of which is excited by a substantially constant voltage in opposite polar relation'to the excitation of the first field system and the other is excited by the resultant voltage of the exciting system in additive polar relation with the excitation of the said first field system.

' I TOSHIICHI I A'GIQ 

